Interstage cooling in the compressor of a gas turbine set is a well-known measure which can substantially contribute to an increase of the efficiency factor and the performance of a gas turbine set, particularly when the heat removed from the partially compressed working medium can be usefully employed at a place in the power station. EP 515 995 proposes in this regard to conduct the compressor air through a steam generator, and thus to produce an amount of steam which can be further used in the water-steam circuit of a combination plant. EP 781 909 and EP 898 645 propose supersaturating the air with water at the compressor inlet, so that a binary air-water-steam mixture enters the compressor. The successive evaporation of the water droplets introduced into the compressor leads to an intensive internal cooling of the compressor; the resulting steam is expanded in the turbine of the gas turbine set, with delivery of power.
Besides a significant reduction of the power uptake of the compressor, the result of a simple consideration of stage kinematics of the compressor is that the interstage cooling furthermore leads to a displacement of the pressure build-up in the rear compressor stages. The article, “Wet Compression: Gas Turbine Power Output Enhancement for Peak-Load Demand”, Siemens Power Journal 1/2000, pages 29–32, states in this regard that this leads to a disequilibrium between the compressor bleed pressures for the cooling air and the turbine pressures which correspond to these. It is proposed on the one hand to correspondingly adjust the diaphragms built into the cooling system for cooling air mass flow adjustment. Alternatively, it is proposed to provide an automatic cooling air regulating system.
With regard to the first proposed variant, it is to be stated in this connection that this leads, in operation without compressor cooling, to a cooling air mass flow which is far above what is required, markedly limiting the power and efficiency factor potentials of the gas turbine set. With regard to the second proposed variant, it is to be stated that the document gives no hint as to how such a control system would be implemented.